Torque-transmitting devices, e.g. magnetic clutches, have been provided heretofore for the selective coupling of a driving element, e.g. a pulley, with a load which can be represented in the form of a shaft upon which the pulley is rotatable.
In many cases it is desirable that the shaft or load be brought immediately to standstill when the driving element is cut off or the clutch is disengaged. For example, in saws or other cutting appliances, presses and the like, practically instantaneous braking of the load is desirable after disengaging of the clutch for the safety of the operator and protection of the equipment.
The rapid or instantaneous braking of the load can be effected magnetically as well.
It is known, in this connection, to provide an armature disk which can be connected to the load, i.e. the shaft, and to additionally provide outwardly of this armature disk, a ring which can be formed with clutch and braking surfaces, means for axially displacing this ring, and a resilient connection between this ring and the armature disk.
The armature disk may be provided with or considered to be an entrainer which can be resiliently or fixedly mounted upon the shaft.
In general, therefore, the invention can be considered to deal with a torque-transmitting unit capable of providing rapid braking, as required, which comprises such an armature disk and entrainer arrangement.
The present assignee (Zahnradfabrik Friedrichshafen Aktiengesellschaft of Friedrichshafen, German Federal Republic) markets a single-face clutch and brake with the designation EK/EB-ER in which a first electromagnet around the single armature disk can be energized to actuate the clutch while a further magnet is energizable to actuate the brake.
The armature disk is angularly fixed to the shaft but can be axially shiftable thereon via a spline arrangement.
This spline arrangement has been found to be disadvantageous because it introduces a location at which mechanical wear can be pronounced. Furthermore, a wobbling movement may be generated in the system.
Another combination of electromagnetic clutch and brake, marketed by the German firm STROMAG (MFE 32) utilizes a relatively thick spring ring in a small diameter region between two rotatable parts, one of which is an armature disk fixed angularly and axially to the shaft, and the other of which is an annular part entrained by a spring angularly upon the armature disk but capable of limited axial movement relative to the latter. Of course, the relative axial mobility of the two parts is highly limited by the relatively thick spring and the rate of reaction of the unit is similarly limited, i.e. a rapid braking action cannot be guaranteed.